1. Field of the Invention
This application generally relates to drilling, and more particularly to a method and apparatus for directional drilling.
2. Description of Related Art
For many years, directional drilling has been a cost efficient and less complex alternative to traditional methods of laying pipelines and tubing in open construction. In directional drilling, a special drill head with a guidance piece is used to produce a pilot hole. The guidance piece may be formed either by an end face of the drill head inclined to the axial direction of the drill head or by a guide body bent at a small angle (less than 5xc2x0) in the axial direction of the drill head behind the drill head. Due to the inclined face or the bend in the guide body, the drilling produced with this drill head runs along a circular line with a large radius of curvature. The order of magnitude of the radius of curvature may be, for example, more than 10 meters, or with long drillings, may be more than 100 meters.
The drill column carrying the drill head may be rotated about its longitudinal axis during the forward advance. In this way, the orientation of the inclined surface of the drill head and the bend of the guide piece, and thus the plane of curvature, may be altered. The course of the drilling may be controlled by altering the plane of curvature.
The pilot drill head may include a magnetic probe with which the position of the drill head may be determined accurately. Passive probes may be used at drilling depths of less than fifteen meters in which their positions may be monitored by a monitoring system at the earth""s surface. At greater drilling depths, active probes may be used. Active probes may be supplied with electric power over an electric connection line running in the drill column. Signals may be exchanged with the monitoring system at the earth""s surface over this line. The position of the drill head may be known by means, for example, such as these probes, so that the course of drilling may be controlled accurately by rotating the drill head about its axis.
Setting and maintaining a certain angle of rotation of the drill column may be essential for controlling the course of drilling. Thus, it is not usually possible to apply rotational movements with the drill column to the drill head to increase drilling capacity. Material removed in producing the pilot hole may be carried away primarily by a wash fluid to which a mud forming additive, such as bentonite in particular, is added. The wash fluid comes out of fluid nozzles in the drill head at a high pressure, such as 100 bar. To increase the capacity for removing cut material, rotation of the drill head may be induced through the wash fluid by means of a turbine-like drive, also known as a mud motor, in particular when a bent or angled control element is used behind the drill head for the control. The wash fluid may also provide support for the pilot hole due to the admixed bentonite while also lubricating the drill column. Bentonite mixed with water may have a pasty gelatinous consistency and therefore may reduce friction on the drill column arranged behind the drill head in the pilot hole.
The axial advance of the drill head may be produced by a driving device at the point of entry of the drill head into the ground, exerting a compressive force on the drill column. Despite the wash fluid (also called a supporting fluid) in the pilot hole, there may be considerable friction on the drill column, in particular with lengthy drilling, such as with distances of more than 100 meters. Therefore, a limited axial pressure may be applied to the drill head over the drill column. Because of the limited axial pressure that may be transferred over the drill column, it may be possible to a limited extent to drill by breaking rocks, for example, by means of drill bits on the drill head that are in contact with the material to be removed with an axial pressure and remove this material because of movements of the drill head. Even with drill heads having a rotational drive, the removal of material may take place mainly through a high-pressure supply of the wash fluid and to a limited extent through the mechanical action of drill bits, such as a rotary cutter. Thus, in producing pilot holes, it is may be difficult to penetrate through harder materials, such as for example, in areas of rock and gravel.
After producing the pilot hole, the drill head coming out of the exit hole of the drilling may be removed from the drill column. It may be necessary to widen the diameter of the hole. To accomplish this, an enlargement bit mounted on the drill column may advanced by the drill column through the pilot hole, for example, by means of the driving device, enlarging the diameter in the process. The wash fluid or supporting fluid also supplied to the enlargement bit under pressure through the channel in the drill column may be responsible for removing most of the material. When working with an enlargement bit, the drill head of the enlargement bit may also be set in rotational motion by the drill column. A supporting pipe which supports the drilling with an expanded diameter may be mounted on the rear end of the head of the enlargement bit. The supporting pipe may also be formed by the pipe which is actually to be laid. The supporting pipe may be pulled passively through the hole due to the force applied to the drill column by the driving device.
In accordance with principles of the invention is a device for directional drilling which increases removal of material and drilling through hard materials. This may be achieved according to this invention by providing a housing between the drill column and the drill head having a receptacle for an axially movable piston and a piston drive to generate strokes of the piston acting on the drill head. A connecting link permits an axial movement between the drill head and the drill column and the channel for the wash medium is sealed at least with respect to the end faces of the piston.
The term xe2x80x9cdrill headxe2x80x9d refers to the part which is in contact at an axial end face with the material to be removed. Axial strokes on the drill head are generated by the axially movable piston in the housing, producing a brief increase in surface pressure between the drill head and the material to be removed. The teeth and tips also provided on traditional drill heads for directional drilling remove larger amounts of material, especially hard material, due to the stroke. The efficiency in removal of material is increased greatly by the percussion mechanism. A connecting link provides for axial movements between the drill head and the drill column transmitting the axial force. In the absence of such a connecting link, strikes would be applied to the drill column mounted on the drill head in addition to the end face of the drill head. Consequently, this would reduce the impact energy for removal of material, because the drill column, which may be several hundred meters long, and the drill head would have to be accelerated together. Additionally, the risk of damage to the drill column would be increased.
The fact that the channel for the wash medium may be separated at least from the end faces of the piston may be taken into account. A wash medium, in particular a supporting medium consisting of bentonite mixed with water flowing around the piston at the end face may prevent a rapid axial movement of the piston. When creating the pilot hole in which a drill column is connected to one side of the drill head, the wash fluid may be transported to the drill head exclusively axially through this drill column. In this case, special measures may be taken to prevent the wash fluid from entering the spaces bordering the end faces of the piston. On the peripheral face of the piston, the wash fluid may optionally flow around it because the wash fluid here may not interfere with the axial movement of the piston. Thus, for example, the wash fluid may be used to induce a rotational movement in the piston at its peripheral face. However, it is also possible to completely separate the wash fluid channel from the piston receptacle by creating one or more separate drillings for the wash fluid in the housing. Finally, a pipe may pass through the piston to transport the wash fluid to the drill head.
Such a supply of wash fluid through the housing for the percussion mechanism may be useful when creating the pilot hole. If the diameter is to be increased by pulling the enlargement bit through the pilot hole by means of the drill column, the percussion mechanism may be mounted on the end opposite the drill column. In this case, the drive for the piston may be provided through the supporting pipe. As an alternative, the supporting fluid may also be supplied through the supporting pipe and the drive supplied with a drive fluid, for example, through the drill column.
Deep-hole hammer drills having an axially movable piston in a housing acting on a cutter (such as a trepan, chisel bit, and the like), the drill head, held in the housing in a rotationally fixed but axially movable position may be found, for example, in European Patent Application EP 96,639 A1. However, there has been a prejudice against a similar design of a directional drilling device, in particular because embodiments may need to supply the wash fluid or supporting fluid through the drill column. The known deep-hole hammer drills are used in drilling straight holes where the drill column has a channel for supplying scavenging air. The scavenging air has an extremely low viscosity even at a high pressure and therefore does not prevent free movement of the axially movable piston. It may be also used as a drive medium for the piston.
In directional drilling, the wash medium generally consists of the supporting fluid with water and a high concentration of bentonite. This type of mud medium greatly impairs the free axial movement of the piston and thus seemed to prevent use of a percussion mechanism. Furthermore, there did not seem to be any need for a percussion mechanism because the material is removed essentially by the wash medium.
The present invention, which may include separating the end faces of the piston perpendicular to the axial movement from the wash medium and recognizes the weaknesses of the directional drilling method when working with harder materials, eliminates the difficulties associated with a percussion mechanism with directional drilling devices.
It may be difficult to drive the piston in the present case with the wash medium because of the gelatinous pasty consistency of the wash medium. An embodiment may include having the wash medium flow around the peripheral surface of the piston in the axial direction causing a rotational movement of the piston by acting on guide ribs arranged on the peripheral surface which act as blades on a turbine impeller. The piston may rotate in the housing with one contact face on a ramp face of the receptacle, with the ramp face extending in the peripheral direction and also obliquely to the radial plane of the housing. Thus, the piston which is driven to rotation may be pushed axially away from the drill head. The rear end face of the piston may be supported against a spring element (e.g. steel spring or a spring action gas cushion), so that at the end of the ramp face the piston is driven forward by the spring force in the direction of the drill head.
As an alternative, the supporting fluid may be kept completely away from the piston. In this case, a different drive may be used for the striking or percussion movements of the piston. An electric piston drive may be used and may be advantageous, especially with a drill head having an active probe which may, for example, use a power supply over a power supply cable. The piston may be designed as an armature and the housing surrounding the piston as a stator of an electric motor. The piston may also be supported by a ratchet in the axial direction. The piston may be driven electrically to rotational motion, which is converted by the ratchet and the rear spring into striking movements. The percussion mechanism may be operated by an electric drive independently of the supply of wash fluid. When drilling through soft layers of soil, removal of material may be accomplished using the wash medium. As soon as harder strata are reached, the percussion drive may be activated in an embodiment.
In an embodiment of the invention in which a second drill column or pipe is mounted on the drill head opposite the drill column, the wash fluid may be supplied through one of the columns and the drive power for the percussion mechanism may be supplied through the other.
An embodiment of the invention may include other drive options that are also conceivable for the piston (e.g. hydraulic or pneumatic drives).
When creating the pilot hole, the drill head may have a probe to determine the position of the drill head. An embodiment of the invention may include a probe arranged behind the receptacle for a piston in the housing in order to minimize damage by strikes of the piston.
An embodiment may include a connecting link to permit axial movement between the drill head and the drill column that may be created by a star-shaped driving profile on a shaft which is connected to the drill head, being held so that it is axially displaceable in a star-shaped recess with a plurality of axially extending grooves in the housing. This results in a form-fitting connection in the peripheral direction, reliably transmitting rotational movements of the housing to the drill head. Free mobility of the drill head with respect to the housing may exist in an embodiment of the invention in the axial direction and may be preferably limited by end stops. During drilling, an axial displacement path of the drill head by a few centimeters may be sufficient to completely transfer the striking energy of the hammer to the base of the drilling.
Such a connecting link may be used to create the pilot hole where the drill column applies a pushing force to the drill head as well as to create the expanded diameter, where the drill column pulls on the enlargement bit. The strikes of the piston may support the advancing action of the drill column and produce small displacements of the drill head in the direction of its free-running with respect to the drill column.
If a second drill column or pipe is pulled or pushed passively through the drill hole by the drill head, an embodiment may also include an elastically deformable damping element for damping the axial forces between the drill head and this passively moving drill column. In this case, the drill head pulls or pushes the drill column in the direction of advance. The strikes of the piston act in the same direction, so that undamped contact between the drill head and the drill column which is pulled or pushed would lead to direct transfer of the piston strikes into this drill column.
The housing of the device according to the present invention having the piston may also at the same time form the control element for controlling the direction of advance of the drill head. In this case, this housing may be designed with a curvature or angle in the longitudinal direction.
The drill head itself may be designed as a guidance head with an inclined face and the housing may be straight. As mentioned above, the device according to the present invention may also be provided with a rotational drive for the drill head itself, preferably driven by the wash medium. Such a rotating drill head may be provided with a curved housing as the guidance element, leading, when combined with the percussion mechanism according to the present invention, to a high-quality rotary percussion drill which represents an innovation in directional drilling and may also result in a considerable increase in capacity.
In accordance with another aspect of the invention is a device for directional drilling. It includes a drill head mounted on a drill column. A driving device applies an axial driving force to the drill column. A delivery device supplies a wash medium to the drill head through a channel in the drill column. A housing arranged on the drill head has a receptacle for an axially movable piston drive for producing strikes of the piston on the drill head. A connecting link permits an axial movement between the drill head and the drill column. The channel for the wash medium is sealed at least with respect to end faces of the piston.
In accordance with yet another aspect of the invention is a device for directional drilling. A drill head is mounted on a drill column. A driving device applies an axial driving force to the drill column. A delivery device supplies a wash medium to the drill head through a channel in the drill column. A housing arranged on the drill head and having a receptacle for an axially moveable piston and a piston drive to produce strikes of the piston acting on the drill head.
In accordance with yet another aspect of the invention is a device for enlarging a pilot hole. A drill head is mounted on a drill column and has an annular working surface. A supporting pipe is mounted on the drill head opposite the drill column. A driving device applies an axially driving force to the drill column. A housing is arranged on the drill head and has a receptacle for an axially moveable piston and a piston drive that produces strikes of the piston acting on the drill head.
In accordance with yet another aspect of the invention is a device for directional drilling. A drill column is mounted on a drill head. A channel is arranged in the drill column that supplies a wash medium to the drill head. Means for connecting the drill head to the drill column permits a relative movement of the drill head to the drill column along a longitudinal axis of the drill head. Pressure means provides a pressure on the drill head being movably arranged along the longitudinal axis and having at least two faces. One of the faces is arranged on the pressure means in a direction to the drill head. The other one of the faces is arranged on the pressure means in the opposite direction to the drill head. At least one sealing seals the faces with respect to the channel.